1. Field of the Invention
The present invention relates to a connecting arrangement for interconnecting upright standards and lateral cross connecting members for supporting scaffolding.
2. Description of the Prior Art
In systems scaffolding rigid tubular members are employed to support elevated walkways and platforms to allow workers to perform tasks at elevated levels. In system scaffolding sections of hollow steel tubing, which may, for example, be two inches in diameter, are employed both as upright and as cross connecting members. The upright tubular members are referred to as uprights standards. At their bases the upright standards are often equipped with screw jacks which can be operated to adjust the elevation of an upright standard.
Upright standards are cross connected together by laterally extending scaffold supports, which are also formed of hollow steel tubing. Lengthy, horizontally disposed laterally extending supports are referred to in the trade as runners, while shorter horizontally disposed members are termed bearers. The bearers and runners are typically four to six feet in length. Runners and bearers are frequently secured to upright standards by means of latching or connecting rings which are permanently secured to the upright standards at spaced intervals therealong. Runners and bearers extend between latching rings at the same elevation on adjacent standards. In addition, diagonal braces interconnect latching rings at certain levels on upright standards to latching rings at different elevations on other upright standards.
In most scaffold latching ring arrangements an annular generally disk-shaped latching ring is welded or otherwise permanently secured to an upright standard. The lateral scaffolding supports are provided with interconnecting brackets at their extremities. These brackets typically have upper and lower horizontally disposed flanges, both of which have vertically aligned openings therethrough. To removably secure a lateral scaffolding support to an upright standard the flanges on the bracket of a lateral scaffolding support are brought into vertical alignment with a latching ring on an upright standard so that the upper flange lies above the latching ring and the lower flange is disposed beneath the latching ring. The brackets are also provided with removable wedge shaped latching members which can be lowered down through the aperture in the upper flange, through a vertically aligned latching opening in the latching ring, and through the aperture in the lower flange. The end of the lateral scaffolding support is thereby releasably attached to the upright standard at a desired elevation.
The ends of the various lateral scaffolding supports are connected to the various rings on a number of upright standards to form a scaffolding structure. Typical conventional scaffold support connecting arrangements are described in U.S. Pat. Nos. 4,493,578; 4,840,513; 4,587,786; 4,394,095; 4,044,523; and 4,180,342, for example.
One problem which has persisted in conventional systems scaffolding connection arrangements in which a wedge is employed to secure the bracket of a lateral scaffolding support to a latching ring is that the conventional systems herebefore available are all capable of being assembled out of square. That is, the coupling mechanisms allow the horizontal lateral scaffolding supports to be coupled at slight deviations from precise radial alignment relative to the upright standards. As the scaffolding increases in number of levels, the slight misalignment is cumulative with each level, so that the levels of scaffolding twist further and further out of square the higher up the scaffolding goes. This departure from precise orthogonal alignment, which is multiplied with each interconnecting horizontal level, can cause the scaffolding to be unstable to the point where it is no longer structurally sound.
Different connecting systems have been devised to attempt to ensure precise orthogonal alignment of the scaffolding members. For example, U.S. Pat. No. 4,044,523 describes a system in which four substantially "barrel shaped" openings are defined in a latching ring. The theory of operation of this system is that even if the flange openings are slightly out of radial alignment with the upright standard to which the lateral supporting member is to be connected, the act of driving the wedge downwardly into the "barrel shaped" latching ring opening will cause the wedge to rotate slightly about a vertical axis so that the increasing width of the portion of the wedge in the radial direction at that level can enter the latching ring opening. The twisting action of the wedge is transmitted to the bracket, which in turn is supposed to bring the lateral support into orthogonal alignment. The structure of the wedge in effect is supposed to act as a lever to rotate a runner or bearer in a horizontal plane. The problem with this system, however, is that the lever arm provided by the wedge is simply too short to perform the desired correction effectively. Since the edge of the wedge which bears laterally against the side of the latching ring opening is no more than one and one half inches from the face of the upright standard or fulcrum point, the lever arm is simply too short to bring a bearer or runner several feet in length into orthogonal alignment. Due to the tolerance in the fit of the wedge into the latching ring opening and the distortion to both the wedge and the latching ring which can result from driving the wedge into the opening at a small angle of misalignment, it is possible for the wedge to be completely seated while the bearer or runner carrying the bracket into which the wedge is driven remains slightly misaligned.
Another system which has attempted to solve the problem of misalignment is described in U.S. Pat. No. 4,587,786. In this system the openings in the latching ring are shaped substantially as truncated arcuate sectors of a circle in which a notch is defined at the center of the radially inwardly facing edge of the latching ring opening. A wedge driven into the latching ring opening is not supposed to seat unless it is centered precisely within the lateral confines in the notch in the outer wall of the opening. However, in this system the front of the wedge closest to the upright standard is not stabilized sufficiently and the tolerances provided by the notch are not sufficient to prevent the wedge from being driven into the latch ring opening at an angle of slight misalignment relative to precise orthogonal, radial orientation with respect to an upright standard.